The T24 steel represents the new generation of low-alloyed creep resistant steels with higher creep resistance andlower carbon content. It was designed as prospective material for membrane waterwalls of ultra super critical (USC)power plants, enabling to avoid preheating and post weld heat treatment (PWHT) during welding. However, ourinvestigations concerning secondary hardening of vanadium containing low-alloyed steels show that non-temperedwelded joints undergo a signifi cant increase in hardness during exposure to operating temperature. The resultsthen imply that PWHT of T24 steel welds is necessary and this idea is at present supported by the occurrence ofseveral troubles with new installations of USC blocks in Europe.
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